1. Field of the Invention
The invention relates to the conversion of kinetic energy of a projectile into thermal energy to slow the projectile via inductive braking. More particularly it relates to an improved inductive-braking apparatus for nondestructive capture of hypervelocity projectiles.
2. Description of Related Art
Inductive braking (also referred to as magnetic braking) relies on the generation of induced magnetic fields to supply braking force to a moving projectile, which has its own magnetic field. The moving field source, associated with the projectile, can be a permanent or electro-magnet secured to a projectile it is desired to stop, moves along a path adjacent a conductor, for example through the hollow bore of a cylindrical sleeve or other long enclosure made of metal or other conductive material. As the field source moves along the conductor length, it induces a flow of currents through the conductor, which in turn generates induced magnetic fields. Typically, two such fields are induced: one behind the projectile having the same polarity as the projectile's field, and one ahead of the projectile having opposite polarity. The induced magnetic field ahead of the projectile repels the field associated with the projectile. The induced field behind the projectile attracts the projectile's field. The effect of these magnetic interactions is to magnetically decelerate the projectile along its path adjacent the conductor, converting its kinetic energy into thermal energy that is absorbed in and can be dissipated from both the projectile and the adjacent conductor.
Inductive braking has been used in some applications. Its use is limited by the field strength of the magnetic-field source in the projectile, because this limits the available braking force. As will be appreciated, the amount of braking force required will depend on the mass of the projectile, its initial velocity and the required stopping distance. The fields produced by permanent magnets may be sufficient for conventional applications, with projectile masses and speeds limited only by the required stopping distance and limitations on brake system mass. However, at the speeds and masses of interest in hypervelocity applications (for example launching payloads from Earth to be retrieved by a receiver in orbit), the fields produced by conventional permanent magnets will not stop projectiles in a practical distance. The field produced by the best permanent magnets is approximately 0.5 Tesla. This will be insufficient to arrest a hypervelocity projectile of even modest mass, or other high-energy projectile, within a reasonable distance.
Increased braking force is desirable to achieve adequate braking of a hypervelocity or other high-energy projectile within a reasonable distance. In addition, it is desirable to ensure that the hypervelocity projectile will not be damaged during deceleration, particularly in hypervelocity applications, for example by impacting the conductor that is used to generate the induced magnetic field.